1. Field of the Invention
The present invention relates to acoustic transducers, and particularly, but not exclusively, to loudspeakers.
2. Description of the Related Art
Both loudspeakers and microphones may be characterised as acoustic transducers, by respectively converting electrical energy into some form of mechanical vibration, or vice versa.
Loudspeaker designs may typically be split into two categories: designs such as dynamic loudspeakers, which use a cone supporting a voice coil which acts on a permanent magnet; and designs such as electrostatic and planar-magnetic speakers, which pass an electrical signal through a thin film, which in turn acts on super high tension stators or magnets to generate vibration.
Similar microphone designs exist, as they are the functional opposite of loudspeakers.
A problem with dynamic loudspeaker designs is that, due to the magnetic field created by the voice coil due to current flowing through it, a back-EMF (electromotive force) is created due to interaction with the permanent magnet's fixed field. This moves the loudspeaker away from being purely resistive in its electrical operation, contributing to non-linearities and distortion of the audio being reproduced.
A problem with thin film-type loudspeakers is that they oscillate in a planar fashion, and so the radiation pattern they exhibit is highly directional, especially at higher frequencies. In addition, they require components for generating a magnetic field to be placed on both sides of the thin film so as to generate a uniform magnetic field. This adds to cost and complexity.